Why This Cyclone is the Bomb

January 4, 2018

Wow. #BombCyclone is now down to 951mb. Likely the most intense East Coast winter storm in the satellite era. (Previous record: 953mb in Feb. 1976)Strengthened 59mb in just 24hrs. Likely the most rapidly intensifying East Coast winter storm on record. (Prev: 49mb in Dec. 1996) pic.twitter.com/862KOLZnKY

Climate change makes the initial conditions all the more favorable for storms like these — higher sea level, more water vapor, intense temperature differentials.

For context on the tweet above, the strongest tropical cyclone recorded worldwide, as measured by minimum central pressure, was Typhoon Tip, which reached a pressure of 870 hPa (25.69 inHg) on October 12, 1979.
At 940 millibars — 27.76 inches — Hurricane Sandy was the lowest barometric reading ever recorded for an Atlantic storm to make landfall north of Cape Hatteras, North Carolina.

When discussing the storm, some weather forecasters have referred to a “bomb cyclone.” Calling it a “bomb” sounds dire, but those kinds of storms are not exceedingly rare — there was one in New England recently.

What makes a storm a “bomb” is how fast the atmospheric pressure falls; falling atmospheric pressure is a characteristic of all storms. By definition, the barometric pressure must drop by at least 24 millibars in 24 hours for a storm to be called a bomb cyclone; the formation of such a storm is called bombogenesis.

Here is how it works: Deep drops in barometric pressure occur when a region of warm air meets one of cold air. The air starts to move, and the rotation of the earth creates a cyclonic effect. The direction is counterclockwise in the Northern Hemisphere (when viewed from above), leading to winds that come out of the northeast — a Nor’easter.

That’s what happened at the end of October, when warm air from the remnants of a tropical cyclone over the Atlantic collided with a cold front coming from the Midwest. Among other impacts then, more than 80,000 electric customers in Maine lost power as high winds toppled trees.

A similar effect was occurring Wednesday, as warm air over the ocean met extremely cold polar air that had descended over the East. Pressure was expected to fall quickly from Florida northward.

[BREAKING] #Boston tide observation on its way to being the HIGHEST EVER RECORDED since 1921; record 4.82' MHHW (or 15.1' MLLW) back w/ the #blizzard of '78; presently at 4.718' (or 14.99') which is the second highest tide ever on record pic.twitter.com/DhMlLUEysI